Chapter 1 Basic Radio Theory

Question 1

Define a hertz

Answer 1

1 complete cycle (1 Hz = 1 wave per second)

Question 2

Define the wavelength

Answer 2

The distance between a peak and the next peak

Question 3

Define phase

Answer 3

The difference in angle between to waves

Question 4

What is the frequency range of very low frequency (VLF)?

Answer 4

3khz - 30khz

Question 5

What is frequency of low frequency (LF)?

Answer 5

30khz - 300khz

Question 6

What is the frequency range if medium frequency (MF)?

Answer 6

300khz - 3mhz

Question 7

What is the frequency range of high frequency (HF)?

Answer 7

3mhz - 30mhz

Question 8

What is the frequency range of very high frequency (VHF)?

Answer 8

30mhz - 300mhz

Question 9

What is the frequency range of ultra high frequency (UHF)?

Answer 9

300mhz - 3ghz

Question 10

What is the frequency range of super high frequency (SHF)?

Answer 10

3ghz - 30ghz

Question 11

What is the frequency range of extremely high frequency (EHF)?

Answer 11

30 ghz - 300ghz

Question 12

What is the speed of light?

Answer 12

300,000,000 m/s (3*10^6)
300,000 km/s
162,000 nm/s

Question 13

What is the formula relation frequency, speed of light and wavelength?

Answer 13

F = c/lambda

F = frequency (Hz)
c = speed of light
Lambda = wavelength (metres)

Question 14

What is modulation?

Answer 14

The process of adding intelligence or information to a carrier wave

Question 15

What are the four types of modulation?

Answer 15

Pulse modulation/keying, amplitude, frequency and phase

Question 16

What does phase modulation require?

Answer 16

A complex demodulator

Question 17

Where is phase modulation used?

Answer 17

In GPS receivers

Question 18

What does modulation create?

Answer 18

Upper and lower frequency known as side bands (e.g. a modulation of 2Hz creates a bandwidth of 4Hz)

Question 19

Why are single side bands used for HF comms?

Answer 19

Reduces the requirement for the power needed to transmit the signal

Question 20

What are the 6 types of antennas?

Answer 20

Dipole, loop, parabolic, phases array, slotted planar array and helical

Question 21

What is the orientation of the magnetic (H) field and the electric (E) field on a vertical antenna?

Answer 21

Magnetic = horizontal
Electric = vertical

Question 22

What is the most basic antenna?

Answer 22

A dipole antenna

Question 23

What does a dipole antenna consist of?

Answer 23

Two unipole antennas

Question 24

How much does each pole contribute to the total wavelength?

Answer 24

One quarter (so dipole = half of the wavelength)

Question 25

What are the three categories of radio waves?

Answer 25

Ground, sky and space waves

Question 26

Where is the weakest reception on a dipole antenna?

Answer 26

Directly above it

Question 27

Define diffraction

Answer 27

The ability of a radio wave to follow the curvature of the earth

Question 28

How does diffraction vary with frequency?

Answer 28

The lower the frequency the greater the diffraction

Question 29

Define attenuation

Answer 29

How much a radio wave deteriorates (high attenuation is bad)

Question 30

What is the main propagation method of HF radio waves?

Answer 30

Sky waves (still some ground waves)

Question 31

What is the relationship between frequency and refraction?

Answer 31

The lower the frequency the greater the refraction

Question 32

How does a radio wave react when it meets the ionosphere?

Answer 32

It refracts (IT DOES NOT REFLECT)

Question 33

Why don’t VHF waves diffract?

Answer 33

Too low frequency

Question 34

What is the attenuation like of VHF waves?

Answer 34

Very high attenuation

Question 35

What are the three alternative names for VHF waves?

Answer 35

Line of sight waves, space waves and direct waves

Question 36

How does attenuation vary with frequency?

Answer 36

The lower the frequency the lower attenuation

Question 37

How does the ionosphere density change during the course of 24 hours?

Answer 37

``` Day = higher density Night = lower density ```

Question 38

What radio waves does the D layer have no effect on?

Answer 38

HF and above

Question 39

What are the two layers in the F layer?

Answer 39

F1 and F2

Question 40

What frequencies pass through the F layer?

Answer 40

UHF and above

Question 41

Beyond the ionosphere how does attenuation vary with frequency?

Answer 41

Higher frequency = less attentuation

Question 42

What layer of the ionosphere do HF refract off?

Answer 42

The F layer

Question 43

What happens to the D layer at night?

Answer 43

It disappears

Question 44

What happens to the E layer at night?

Answer 44

Moves higher up

Question 45

What happens to the F layer at night?

Answer 45

They merge into one

Question 46

What happens to both the E and F laters at night?

Answer 46

Become thinner and less dense

Question 47

What happens to the amount of refraction at night?

Answer 47

Refraction reduces due to the lower density of the layers

Question 48

How are radio waves frequencies changed at night?

Answer 48

Lower the frequency

Question 49

During the day what waves does VLF produce?

Answer 49

Ground and sky waves

Question 50

During the night what waves does VLF produce?

Answer 50

Ground waves

Question 51

What is the critical angle sky wave?

Answer 51

The min angle at which the radio wave will refract and return to earth

Question 52

What is the skip distance?

Answer 52

Distance between the transmitter and the point where the first sky wave arrives

Question 53

What is the dead space area?

Answer 53

Area between the limit of the ground waves and the first sky wave

Question 54

How is the dead space area reduced?

Answer 54

Reduce frequency

Question 55

How is the critical angle reduced?

Answer 55

Lower frequency

Question 56

What causes super refraction?

Answer 56

A temperature inversion and/or rapid decrease in humidity with height

Question 57

What are is the effect of super refraction?

Answer 57

Unexpected VHF ranges